A combustion turbine typically includes, in a serial flow relationship, a compressor section to compress the entering airflow, a combustion section in which a mixture of fuel and the compressed air is burned to generate a propulsive gas flow, and a turbine section that is rotated by the propulsive gas flow. After passing through the turbine section, the propulsive gas flow exits the engine through a diffuser section. In ground based combustion turbines used for electricity generation, power is normally extracted from the rotating shaft to drive an electrical power generator.
The efficiency of a combustion turbine is related to the combustion temperature. In the pursuit of greater combustion turbine efficiency, components formed from new materials are desired to withstand the increased temperatures that often accompany an increase in efficiency. Likewise, new cooling methods are desired to cool the components.
An exhaust diffuser section of a ground based combustion turbine is commonly subjected to temperatures in excess of 1000° Fahrenheit. One approach to improving diffuser performance, the insertion of vortex generators into the diffuser, is disclosed in U.S. Pat. No. 6,682,021 to Truax et al. Vortex generators may need a high momentum fluid flow to re-energize the boundary layer and enhance attachment. Since the fluid flow may slow as it travels from the diffuser inlet to the diffuser outlet, the fluid flow available to a vortex generator closer to the diffuser outlet may be unable to sufficiently re-energize the boundary layer to prevent separation.
U.S. Pat. No. 6,896,475 to Graziosi et al., for example, discloses a diffuser for a gas turbine having an outer wall, a centerbody, and a strut extending therebetween. The outer wall and centerbody each have an opening, in the vicinity of the diffuser inlet. The gas turbine directs a steady stream of fluid from an upstream turbine stage to the openings to prevent or delay boundary layer separation.
Another approach is presented in U.S. Pat. No. 5,603,605 to Fonda-Bonardi, which discloses the placement of a capture scoop located in the vicinity of the outlet of a diffuser section of an axial gas turbine. Fluid collected by the capture scoop is fed to a plurality of slots in the inner and outer walls of the diffuser section to re-energize the boundary layer. The slots of this approach may not be able to deliver enough fluid to re-energize the boundary layer at all points and prevent detachment because the volume of fluid delivered through the slots depends upon the volume of the fluid in the diffuser.